The stereoselectivities of organic reactions will be investigated theoretically in order to develop reliable qualitative and quantitative techniques to predict stereoselectivities and to design useful new reagents and catalysts. The success of this work should facilitate the efficient synthesis of pharmaceutical agents and will eventually help elucidate the origins of enzyme stereospecificity. In previous years of support, we have developed empirical transition state models based upon quantum mechanical transition structure calculations, and we have shown how these can be used to understand rates and selectivities of many types of organic reactions. This proposal describes the progress which has been made and summarizes the state of the art in modeling stereoselectivities of organic reactions.